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WARP1: Towards walking in rough terrain: control of walking
KTH, Superseded Departments, Machine Design.
KTH, Superseded Departments, Machine Design.
2003 (English)In: Climbing and walking robots: and their supporting technologies, 2003, 467-474 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper describes further results from making the four-legged robot WARP 1 capable of walking in rough terrain. In this work, WARP1'S special foot length sensors (FLS) are used to improve leg control during footfall, footlift and support. It is shown that using the FLS can reduce the duration of a footfall without increasing disturbances on the trunk. This strategy has been used for walking over obstacles, as described in a companion paper.

Place, publisher, year, edition, pages
2003. 467-474 p.
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-9029ISI: 000186071100056OAI: oai:DiVA.org:kth-9029DiVA: diva2:14568
Conference
6th International Conference on Climbing and Walking Robots (CLAWAR 2003) CATANIA, ITALY, SEP 17-19, 2003 Themat Network CLAWAR 2
Note
QC 20100831Available from: 2006-01-26 Created: 2006-01-26 Last updated: 2010-12-07Bibliographically approved
In thesis
1. Quadruped robot control and variable leg transmissions
Open this publication in new window or tab >>Quadruped robot control and variable leg transmissions
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The research presented in this thesis regards walking of quadruped robots, and particularly the walking of the Warp1 robot. The motivation for the robot is to provide a platform for autonomous walking in rough terrain.

The thesis contains six papers ranging from development tools to actuation of robot legs. The first paper describes the methods and tools made for control development. These tools feature: programming of the robot without low level coding (C-code); that the controller has to be built only once for simulation and experiments; and that names of variables and constants are unchanged through the chain of software Maple -- Matlab -- Simulink -- Real~Time~Workshop -- xPC--Target.

Three controllers, each making the robot walk are presented. The first controller makes the robot walk using the crawl gait. The method uses static stability as method for keeping balance and the instantaneous trunk motions are given by a concept using the so called weight ratios. A method for planning new footholds based on the positions of the existing footholds is also proposed and the controller experimentally verified.

The second walking controller shows that the robot also can walk dynamically using the trot gait. The method proposed uses information from ground contact sensors on the feet as input to control balance, instead of, which is common, inertial sensors. It is experimentally verified that Warp1 can trot from level ground onto a slope and turn around while staying balanced.

The main ideas of these two walking controllers are fused in the third which enables smooth transitions between crawl and trot. The idea of using the ground contact sensors from the first controller is here used to estimate the position of the center of mass. This controller uses weight ratios in the gait crawl as well as in the dynamic gait trot. Hence, the method of using weight ratios is not only useful for static stability for which it was originally intended. The controller is experimentally verified on Warp1.

The Warp1 robot weighs about 60 kg, has 0.6 m long legs with three actuated joints on each. The speed and strength is sufficient only for slow walking, even though the installed power indicates that it should be enough for faster walking. The reason is that a walking robot often needs to be strong but slow when the feet are on the ground and the opposite when in the air. This can not be achieved with the motors and transmissions currently used.

A transmission called the passively variable transmission (PVT) is proposed which enhance motor capabilities of robot joints. It is elastic, nonlinear and conservative. Some general properties for elastic transmissions are derived such that they can be compared with conventional transmissions. The PVT gives strong actuation at large loads and fast actuation at small loads. The proposed transmission is compared to a conventional transmission for a specific task, and the result is that a smaller motor can be used.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xii, 50 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2006-02
Keyword
walking robot, quadruped, walking, crawl, trot, passively variable transmission, PVT, variable transmission, continuously variable transmission, velocity ratio, torque ratio
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-600 (URN)91 7178 257 5 (ISBN)
Public defence
2006-02-10, M2, Brinellv. 64, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100831Available from: 2006-01-26 Created: 2006-01-26 Last updated: 2010-08-31Bibliographically approved

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